Does anyone knows how a program like phonefree works???

Does anyone knows how a program like phonefree works???. I will explai
what phone free is. Phone free gives you the ability to call while your on
the internet. So you can make long distance calls paying a lot less (If you have
cable you can call for free for example). How can such a program establish
a connection when your on the internet? Does anyone know how to call or dial
a number while on ther internet, or knows or program wich I can put on a surfer
and that program can dial a number when I request ????